Medical vascular catheters are particularly designed and available for a wide variety of purposes, including diagnosis, interventional therapy, drug delivery, drainage, perfusion, and the like. Medical vascular catheters for each of these purposes can be introduced to numerous target sites within a patient's body by guiding the catheter through an incision made in the patient's skin and a blood vessel and then through the vascular system to the target site.
Medical vascular catheters generally comprise an elongated, flexible catheter tube or body with a catheter side wall enclosing a catheter lumen extending between a catheter body proximal end coupled to a relatively more rigid catheter hub to a catheter body distal end. The catheter body may be relatively straight or inherently curve or curved by insertion of a curved stiffening wire or guide wire through the catheter lumen. The catheter body and catheter side wall are typically fabricated and dimensioned to minimize the catheter body outer diameter and side wall thickness and to maximize the catheter lumen diameter while retaining sufficient side wall flexibility and strength characteristics to enable the catheter to be used for the intended medical purpose.
The catheter hub functions as a connector to allow quick connection of a syringe or the like with the catheter lumen. The catheter body distal end may be formed with one or more side wall opening formed in a segment typically adjacent the catheter body distal end and/or with a distal end opening axially aligned with the catheter body. Or the catheter body may additionally or alternatively have further structure formed on the catheter body side wall, e.g., an expandable balloon for dilatation of a blood vessel or installation of an expandable stent or graft, or a sensor, or a therapeutic or diagnostic device. Moreover, the catheter body may include two or more catheter lumens communicating with access ports formed in or extending from the catheter hub to such opening(s) or structure(s).
Often much manipulation is required to guide such catheters through the incision and/or introducer lumen and then through the vascular system to the target site in the body to effect the medical procedure. This manipulation is effected by grasping the catheter body and/or the catheter hub extending outside the body and pushing and twisting it to advance the catheter body distal end through twists and turns of the blood vessel. This manipulation strains and stresses the catheter body, particularly at the catheter body proximal end where the relatively flexible and thin catheter side wall exits from a hub lumen.
Further, the introduction of the vascular catheter into the vascular system may not be the time at which the greatest strain is placed on the catheter hub/body junction. Often, after the catheter body is fully advanced to the target site, the healthcare provider will raise the catheter hub away from the patient's skin in order to insert a smaller catheter or guide wire or the like or a syringe into the hub lumen proximal end opening or to connect a further device to the hub fitting. This raising of the catheter hub places a large bending strain on the catheter hub/body junction, and the catheter body can bend sufficiently to buckle or kink in this area as a result. Or, in a chronic implantation, such kinking can occur at the catheter hub/body junction when the patient rolls over in bed.
In one approach, the hoop strength of the catheter body is maximized at least in a proximal segment thereof. However, this approach stiffens the catheter body and can require a reduction in the catheter lumen diameter. If the full length of the catheter body is stiffened to make it more resistant to kinking, then the stiffness can make the catheter body less maneuverable, particularly in tortuous pathways and through small blood vessels and can cause damage to the vessel walls. A great deal of effort has been expended in developing catheter side walls trading off factors of hoop strength, flexibility catheter body outside diameter, side wall thickness, etc., that affect flexibility, column strength, and maneuverability, and still resist catheter body kinking and minimize damage to blood vessel walls. For example, as described in U.S. Pat. No. 5,066,285, the tubular sheath of a catheter sheath introducer is made of expanded, fibrous polytetrafluoroethylene (PTFE) so as to produce a more flexible sheath having a high hoop strength that allegedly resists kinking. In U.S. Pat. No. 3,618,613, related to a drainage catheter not intended to be inserted through a blood vessel. the tube side wall is reinforced by an embedded wire spring coil. Similarly, uses of embedded wire spring coils to reinforce a medical vascular catheter are disclosed in U.S. Pat. Nos. 4,634,342 and 4,705,511. These reinforced catheter sheaths are helpful in situations where the advancement causes the strain, such as when introducing the catheter through scar tissue. Specialized catheter bodies fabricated to solve the tendency of the catheter body to kink at the catheter hub/body junction are often more difficult to produce and costly to manufacture than uniform catheter bodies.
Despite these efforts, a strain relief is usually incorporated into the catheter hub/body junction in an effort to prevent such kinking of the catheter side wall during installation and use as shown, for example, in U.S. Pat. No. 5,599,325. Strain reliefs are traditionally formed of a bridging material that is more flexible than the catheter hub and less flexible than the catheter body and surrounds a proximal segment of the catheter body to reinforce it. The strain relief is typically attached at the proximal strain relief end to the catheter hub and extends along the proximal catheter body segment to a distal strain relief end. The object of the strain relief is to prevent concentration of the bending forces at the catheter hub/body junction by resisting and dissipate applied bending forces along the length of the strain relief, and thereby prevent collapse of the catheter side wall and kinking of the catheter body. The strain relief thereby functions to "relieve" the strain at the catheter hub/body junction by spreading bending forces along a larger length of the catheter body.
The bending force and kinking problems are described in U.S. Pat. Nos. 5,167,647, 5,330,449, and 5,380,301 for example, incorporated herein by reference, and addressed by use of tubular sheath strain reliefs surrounding and extending distally from the catheter hubs. In the '301 patent, the strain relief is incorporated with a locking mechanism that is alleged to reduce or eliminate any tendency of the release of the catheter hub from the catheter body proximal end due to excessive force applied axially between them. Similar tubular strain reliefs are disclosed in U.S. Pat. No. 5,507,732 and in the above-referenced '325 patent. The tubular sheath strain relief may be tapered from the proximal strain relief end to the distal strain relief end to increase flexibility distally.
Alternatively, the use of coil springs having a spring lumen receiving a distal segment of the catheter body have been disclosed in U.S. Pat. Nos. 4,610,674 and 5,466,230, for example. At least the proximal section of the coil spring disclosed in the '230 patent and the entire length of the coil spring disclosed in the '674 patent are embedded within a tubular sheath or the strain relief. As noted in the '230 patent, the coil spring can either be square or round and formed of a metal or plastic material. In both cases, the coil wire diameters are constant through the length of the coil spring.
In a further approach, convoluted plastic strain reliefs have been incorporated into vascular catheters sold by SciMed Life Systems, Minneapolis, Minn., (an affiliate of Boston Scientific Co.) under the trademarks "Cyber" and "Wiseguide". In these SciMed Cyber and Wiseguide guide catheters, the strain relief takes the form of a series of rings formed around the catheter body and extending along a proximal segment thereof that have ring diameters that decrease distally. The rings are spaced apart from one another but connected with one another at points, e.g., at 180.degree., around the circumference of the catheter body by bridging elements. The strain relief thus resembles a common strain relief used on computer keyboard cables. This type of strain relief does not afford a uniform degree of flexion and kinking resistance around the entire 360.degree. circumference of the catheter body surrounded by it. The bridging elements distort the bending flexibility so that the strain relief bends more readily when bent at 90.degree. to each such bridging elements.
It is therefore well known that the catheter hub/body junction is highly susceptible to strain due to intentionally or inadvertently applied bending forces and that a wide variety of strain reliefs have been employed in the attempt to address this problem. Despite the considerable effort in designing strain reliefs at the catheter hub/body junction, problems still occur with kinking of the catheter body either within the length of the strain relief or just distally to the distal strain relief end.